Method for increasing rate of coating using vaporized reactants

ABSTRACT

A glass substrate is coated with a metal-containing coating by heating the glass and contacting the hot glass with a gaseous mixture. The mixture is from 50 to 100 percent saturated with the vapors of a reactive metal compound at its temperature immediately before contacting the glass. The mixture is heated by the glass to a sufficient temperature causing the metal compound to react thereby depositing the coating.

1: ite States Bless et a1.

atent H 1 [451 Dec. 3, 1974 METHOD FOR INCREASING RATE OF COATING USINGVAPORIZED REACTANTS [75] Inventors: Karl H. Bloss,

Dietzenbach-Steinberg; Harald Molketin, Frankfurt, both of Germany [73]Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Dec. 15, 1972 21 Appl. No.: 315,384

[52] US. Cl...-...; 117/106 R, 117/123 A, 117/124 A [51] I lint. C1.C23c 1l/08 [58] Field of Search 117/106 R, 107.2 R, 107.1,

[56] References Cited UNITED STATES PATENTS 2,430,520 11/1947 Marboe117/106 R X 2,556,316 '6/1951 Cartledge 260/429 J 2,694,651 11/1954Pawlyk 117/106 R 2,898,227 8/1959 Drummond 117/107.2 X 2,933,475 4/1960Hoover et al. 260/429 1 3,356,527 12/1967 Moshier et a1.... l17/107.2 R3,410,710 11/1968 Moche1 117/106 R X 3,438,803 4/1969 Dubble et a1.118/48 X 3,658,568 4/1972 Donley 117/106 R X Primary ExaminerRa1ph S.Kendall Assistant Examiner-Harris A. Pitlick Attorney, Agent, orFirm-Russell A. Eberly 5 7 ABSTRACT 2 Claims, N0 Drawing s METHOD FORINCREASING RATE OF COATING USING VAPORIZED REACTANTS CROSS REFERENCE TORELATED APPLICATIONS This application is related to the followingcopending applications, all commonly assigned, all specificallyincorporated by reference herein and all filed on even date herewith:Nozzle for Chemical Vapor Deposition of Coatings, Ser. No. 315,394,filed Dec. 15, 1972 by Krishna Simhan; Chemical Vapor Deposition ofCoatings, Ser. No. 315,393, filed Dec. 15, 1972, by John Sopko andKrishna Simhan; and Coating Composition Vaporizer, Ser. No. 3l5,395,filed Dec. 15, 1972, by John Sopko.

This application is also related to a copending appli cation entitled AProcess for the Deposition of Films, Ser. No. 182,993, filed Sept.23,1971, and now abandoned based on a convention priority date of Sept.29, 1970, by I-Ians-Jurgen Gotze, Helmut Lukas and Harald Molketin. Thisapplication is also incorporated by reference herein.

BACKGROUND OF THE INVENTION This invention relates to coatingsubstrates, particularly glass substrates, with coatings comprisedprimarily of metal oxides. This invention more particularly relates tocontacting a hot glass surface with the vapors of reactants which formmetal oxide coatings upon cntacting the hot glass surface.

Prior to the present invention, it has been known that substrates may becoated with metal oxide coatings by contacting the substrates withsolutions comprised of metal betadiketonates and the like dissolved inappropriate solvents. See the following US. Patents: Mochel, US. Pat.No. 3,202,054, Tompkins, U.S. Patent'No. 3,081,200, Donley et al, US.Patent No. 3,660,061 and Michelotti et al, U.S. Patent No. 3,652,246.These patents have disclosed to the public a number of chemicalcompositions which are suitable for the coating of glass metal oxidecoatings. In general, the techniques described for applying suchcoatings to glass taught in the prior art are methods wherein a liquidspray of coating composition is directed against a glass substratesurface to be coated. While these patents cover the application ofparticular metals or metal oxides to glass or other substrates, whetherthe compositions are applied in liquid or vapor form, they eachdisclose, as a best mode of application, contacting the substrate withthe composition in liquid form. In the development of techniques forapplying vaporized coating compositions to heated substrates atatmospheric pressure, certain difficulties have been encountered. It hasbeen difficult to obtain coatings which grained and finely and uniformin appearance. Thick coatings have been produced by contacting thesubstrate with a liquid spray, but it has been extremely difficult, ifnot impossible, to obtain relatively thick films having visible lighttransmittances of below about .50 percent using known vapor depositiontechniques. 1

Vapor deposition processeshave been known in the past. Most commercialembodiments of vapor deposition processes are processes carried outunder subatmospheric pressure conditions. In the past, the rate ofdeposition has been controlled or enhanced by increasing the temperatureof the substrate being coated or increasing the temperature of thecoating composition.

Severe limitations have been encountered using such techniques. Forcommonly used materials, deposition rates abruptly cease to increasewith increasing temperature while the coatings produced remain thin.Attempts to increase the activity of the coating generally result inpremature reaction and apparently autocatalytic decomposition of thereactants with coating efficiency actually decreased.

The applicants have now discovered that the uniformity of films producedby chemical vapor deposition and the rate of chemical vapor depositionor film buildup may be significantly enhanced by vaporizing reactantsinto a gaseous carrier in sufficient quantity to approach saturation ofthe carrier and by then directing the mixture against the substrate tobe coated.

SUMMARY OF THE INVENTION A vaporizable coating reactant having anentropy of vaporization of at least about 40 Clausius is mixed with ahot carrier-gas and is vaporized without substantial decomposition inthe gas mixture due to its intimate contact with a hot carrier gas whichthen carries the vaporized coating reactant into contact with'a hotsubstrate causing the reactant to deposit a coating on the substrate.The coating reactant isvaporized in a sufficient amount to provide acoating reactant gaseous carrier mixture which is from about 'to aboutpercent saturated with coating reactant. The advantages of the presentinvention are particularly apparent in the instanace of coatingreactants which autocatalytically decompose at temperatures onlyslightly above their effective vaporization temperatures. When employingsuch reactants, they are preferably dispersed into a hot carrier gas andvaporized by the heat of the gas. By dispersing such reactants in agaseous phase the autocatalytic effect of some isolated decomposition isvirtually eliminated, and by vaporizing from a fog or smoke of reactantin gas the vaporization efficiency is sufficiently enhanced so as to bepractical at lower temperatures.

As already indicated, the coating reactants useful in this invention aredefined by their entropies of vaporization. As used throughout,vaporization includes both sublimation and evaporation. The significanceof this criterion may be appreciated from the following discussion.Coating processes involving hydrolytic or pyrolytic reaction aretopochemical in nature; that is, the coating reaction at the surface ofa substrate must proceed preferentially to reactions in the vicinity ofthe substrate but not in sufficiently close proximity thereto for theproducts of reaction to adhere to the substrate and to themselves toform a coating. The heterogeneous nature of such reactions suggests thatcoating reactants having reactions that are catalyzed by the products ofreaction are preferred for coating. The drawback to such reactants isthat reactions initiated remote from a substrate to be coated canproceed rapidly out of control and, by causing massive decomposition, destroy all coating effectiveness. In order, to avoid this massivedecomposition, sufficient coating reactant must be vaporized at atemperature as low as possible while obtaining a high concentration ofcoating reactant in the gas or vapor which contacts the substrate to becoated. Localized excessive concentration of a coating reactant isbelieved to result in recondensation of coating reactant at lowtemperatures about the vaporization temperature and to result in massiveautocatalyzed decomposition at high temperatures. Reactants which arecharacterized by high entropies of vaporization are believed to diffuseso easily into any carrier gas employed so as to avoid localizedexcessive concentra- In a most preferred embodiment, the carrier gas issupplied at a first temperature and the coating reactant is dispersedinto it under conditions such that the mixture is about 100 percentsaturated upon mixing. The mixtion. Such coating reactants are found tohave vapor 5' ture is then conveyed away from the point of mixingpressures that increase sharply below their decomposiand vaporizationand is heated to a slightly higher temtion temperatures so that steepconcentration gradients perature (5 to C. higher). The mixture may thenbe may be established in the vicinity of intended reaction conveyed tothe substrate to be coated without danger in contact with a substrate tobe coated. of inadvertent condensation of reactant yet with a pre- Thereactants to be employed in this invention may 10 cisely controlledquantity of reactant being maintained be combined with a carrier gas inlarge quantities within the mixture. out saturating it at atmosphericpressure and the tem- Using a gas saturation method, vapor pressures,equiperatures employed for vaporization and delivery of librium vaportemperatures and vaporization enthalthe mixture into close proximitywith a hot substrate. pies were determined for potential coatingreactants. But, because the vapor pressures of these reactants rise Thevaporization apparatus comprised a jacketed glass so sharply withtemperature, their activity is disproporvessel thermostated bycirculatmg hot oil. Test subtionately high with respect to theirconcentration in the stenees were vaporized e fixed Pressure Streams ofimmediate thermal boundary layer adjacent a hot subg heated to deslrefitemperatures- Flow rates strate to be coated. Thus, the coatingdeposition rate is W meaured- The veperlzed Substances f P enhancedbecause of the cooperation between the therlted e" fmted absorptlentraP5 Charged fi Solventl b d layer dj a h substrate to b Ind1v1dualtrapped substances were diluted w1th solvent coated and the particularcoating reactants employed. to filed Volumes and e q PQ analyzed y Thethermal boundary layer may be considered to be vemlonfll spectroscoplctechmque to defermme a relatively quiescent layer of gas adjacent thehot amount of substance transferred. Convenhonal calorlstrate to becoated in which the temperature increases meme techmques Welded enthalpyP asymptotically from the ambient coating chamber temconvemlonalthermefiynamle eenslderetlens yield perature (bulk gas temperature) offrom about 200C. the followmg relatlonshlps' to about 300C. to thesubstrate surface temperature of log P log P AH /R l/T l/T from about400C. to about 600C. The apparent thickand ness of such a layer is belowabout 1 millimeter. Coat- AS AH /T ing reactants moving to the substratethrough this layer where and waste products moving away through it arebe- P and P are vapor pressures in torr at T and T lievedto betransported primarily by diffusion as evi- T, T and T are absolutetemperatures in degrees denced by the superior performance obtained whenKelvin; practicing this invention. R is the gas constant;

In the preferred practice of this invention, a carrier A H is theenthalpy or heat of evaporation in calories; gas, which may be an inertgas or a highly reactive gas but which is preferably air, carriessufficient vapors of A S is the entropy of evaporation in Clausius. areactive coating compound to cause the mixture to be From theserelationships and the experimental data 0bfrom to 100 percent saturated,and preferably from tained, the coating reactants suitable for use inthis into percent saturated. This degree of saturation is vention aredetermined. The properties of these materipreferred to complete percentsaturation because als and other tested materials are summarized inTables the amount of reactant is thereby controllably varied. l and 2.

' TABLE 1 .VAPORIZATION DATA Substance 5... m, 4 ar p- K kcal ClausiusC. C. C. K. Fe(acac), 569 28.6 50.3 296 I88 I08 Fe(acac);, 582 26.9 46.3309 190 119 Fe(F,acac 473 31.6 66.8 200 120 so FC(FQ3CBC); 522 15.5329.8 249 55 195 came 588 27.4 46.6 315 214 101 can-awe), 512 25.4 49.6239 84 Ni(acac), 698 22.9 32.8 425 235 190 Co(acac), 643 19.5 30.3 370130 190 'C0(F,acac), 493 25.5 51.8 220 110 110 C0(aCaC); 622 25.5 41.1349 210 139 Co(F,acac), 523 26.2 50.1 250 90 Mn(acac), 767 I 20.8 27.1494 60(dec.) Mn(acac), 582 26.9 46.2 309 172 137 Cu(acac), 614 26.4543.4 341 230(dec.) (111 TABLE VAPOR PRESSURES (TORR) Substance l00C120C. [40C. l60C. C 200C.

Fe(ucnc), 1.4. 10-= 9.5 10-= 4.9. 10* 2.8. 10- 1.2 4.5 Home), 1.1 10*7.2. 10- 3.7. 10- 1.8. 10- 7.3 10- 2.8 Fe(F,acac), 1.1 10- 0.132 6.0 3.510 1.7. 10 7.6 10

TABLE 2 -Continued VAPOR PRESSURES (TORR) Substance 100C. 120C. [40C. I160C. 180C 200C.

Fe(F,,acac);, 1.9 5.2 1.4 10 3.4 10 7.5 10 1.6 l Cr(acac), 1.1 7.0 10'3.9 10' 1.8 l0 7.0 l0" 2.6 Cr(F acac) 5.8 10 3.4 10' 1.8 7.4 2.7 10 9.510 Ni(acac), 4.3 10' 2.3 10 a 9.5 10 8.0 10" 1.1 10" 3.2 10' Co(acac),1.2 10 4.6. 10 1.6. 10' 4.6. 10 1.2 3.1 CO(F3aCaC)g 1.6 10" 9.6 1Q 4.61.95 10 7.10 2.6 10 Co(acac), 8.7 10" 4.8 10' 2.4. 10 1.0 l0 3.5 10' 1.2C0(F,acac) 3.4. 10 1.9. 10' 9.5. 10" 4.3 1.5. l0 5.3 10

The entropies of vaporization presented in Table 1 range from less than30 to almost 70 Clausius. Since the materials of Table 1 are solids atroom temperature, these may be characterized more specifically asentropies of sublimation. It will be noted that these entropies are allwell above the 22 to 25 Clausius span which embraces non-associating,nondissociating substances.

tion points exceed the melting points of the triacetylacetonates byroughly equivalent spans, all less than 140C. Since the solid complexesare thermostable enough to permit their melting points to be recorded,the vaporization-melting point span represents the approximate range inwhich the thermolabile liquid particles burst into the lessheat-sensitive vapor. This range may be considered a range of thermaljeopardy, that is, it is in this temperature range in which thematerials have sufficient heat and are sufficiently compact thattheirautocatalytic decompositionis greatly risked before they may bewidely dispersed in a vapor phase.

The bis-acetylacetonates of manganese,. nickel and cobalt are noted tohave distinctly smaller entropies of vaporization and to haveconsiderably greater spans of melting point temperature to vaporizationpoint temperature, so that fusion rather than flash vaporization islikely with such materials. The iron Il-acetylacetonate,-however, withan entropy of vaporization of 50.3 Clausius and with a thermal jeopardyspan of 108C. resembles the triacetylacetonates, and so an iron1l-acetylacetonate anomaly is observed.

The fusion of materials is detrimental to vapor coating because, oncefused, the materials remain in a close mass, while their temperatureincreases, and may decompose rather .than'vaporize'from a sticky, fusedmass. in contrast,powders which have a narrow melting point or fusionpoint to vaporization point span may be dispersed as powders into a hotstream of gas and have their temperature quickly raised to thevaporization temperature, with possibly some fusion occurring butwithoutmassive agglomeration of particles into a fused mass that has itstemperature increased to a decomposition point and without substantialvaporization.

Mixed oxide coatings are preferably prepared from materials having theirvaporization parameters (entropy of vaporization and thermal jeopardyspan) closely related to one another. For example, thetriacetylacetonates of chromium, manganese, iron and cobalt all haveentropies of vaporization which are 46 i 5 Clausius, and all havethermal jeopardy spans which are 120 i 20 C. By the same token, nickeland cobalt acetylacetonates are favored for combinations.

Trifluoroacetylacetonates show quite advantageous characteristics forchemical vapor deposition. The span between melting point andvaporization point is quite small, being only C., and the entropy ofvaporization, e.g., of iron-Ill trifluoroacetylacetonate is 66.8Clausius, which is almost 50 percent greater than the entropy ofvaporization for the fluorine-free iron lll-acetylacetonate The ironlll-trifluoroacetylacetonate powder can be vaporized efficiently in apowder vaporizer, and its partial pressure is increased to atmo' sphericpressure before any pyrolysis of individual particles is detected.

While the discussion above points out the importance of vaporizationentropy of coating reactants as affecting the usefulness of particularcompounds for chemical vapor deposition, the significance of carrier gassaturation is more particularly pointed out in the following examples.In the following examples, soda-lime-silica glass plates are coated bypyrolysis of the coating reactants tested. in all examples, glass platesare clamped to a heated traversing mechanism disposed within a coatingchamber and passed beneath a slot through which a gaseous mixturecontaining vapors of coating reactant is passed and directed against theglass plates. 7 In all instances, the exposed plates have exposed areasfor coating, measuring 24 square inches. The coating reactants arepowdered and fed into a heated tubular chamber leading to the slotfacing the glass specimen. A carrier gas is heated and directed into thetubular chamber to carry the coating reactant and vaporize it as itpasses through the chamber to the slot for dis charge against thespecimen to be coated. The'amount of coating reactant delivered to thechamber, the flow rate of carrier gas, the duration of deposition, thetemperature of the carrier gas in the tubular chamber and thetemperature of'the glass specimen are all measured during coating. Aftereach specimen is coated, the

, coating is chemically stripped from the specimen and the quantity ofmetal in the coating is determined by conventional atomic absorptionanalysis. The total supply of metal provided is known, and the size ofthe slot in relation to the glass specimen is such that blowby materialmay be ignored.

EXAMPLE 1 Using a slot having a width of 3 millimeters and a length of 5millimeters, carrier gas is supplied at a rate of 7.6 liters per minuteand the source temperature is adjusted to establish a constant vaporpressure of 5.7 X torr when powdered iron lI-acetylacetonate wassupplied by a screw feeder to a pipe surrounded by a resistance heater.This heated pipe is connected to the slot. The substrate temperature isvaried for each series of specimens by controlling the temperature of ahot plate supporting it in order to establish the effect of substratetemperature upon deposition rate. In a first a series, the substratetemperature is 300C, and in each succeeding series the substratetemperature is raised by C. Analysis of the resulting coated specimensshows that deposition rate, as represented by micrograms of metal persquare centimeter, is substantially independent of glass temperatureabove about 400C. This demonstrates that the substrate temperature,which has been known in the past to be important to deposition rate, isnot a limiting factor in chemical vapor deposition. The coating reactantemployed must have greater activity due to greater effectiveconcentration near the substrate surface in order to cause greaterreaction rates, for the evidence shows that this is a more importantlimiting factor. The full results of this example are presented in Table3 below.

EXAMPLE 11 The procedure of Example 1 is repeated, except that ironIll-acetylacetonate is employed at a vapor pressure of 2.9 X 10 torr.Again, the substrate temperature is found not to be a limiting factor incoating rate. The full results of this example are also presented inTable 3.

EXAMPLE 111 The procedure of Example 1 is again repeated, except thatnickel l1-acety1acetonate is employed at a vapor pressure of 3.4 X 10torr in this example, and again, temperature is not found to be limitingabove about 450C. The full results of this example are also presented inTable 3.

TABLE 3 Glass Temperature Deposition Rate C. Micrograms/CentimeterFe(acac) Fe(acac); Ni(acac)z LII The procedures described in Examples 1,11 and 111 were repeated, using cobalt II-acetylacetonate, cobaltlll-acetylacetonate, iron lll-trifluoroacetylacetonate and chromiumIII-acetylacetonate. The temperature EXAMPLE 1V lron lll-acetylacetonateis used to deposit iron oxide coatings on a series of specimens in orderto demonstrate the significance of carrier gas saturation upondeposition rate. The coating reactant is vaporized from a powder at 116C., and the carrier gas is supplied at two different rates; namely,7.6 liters per minute and 21.8 liters per minute. If the degree ofsaturation were not a factor, the performance of the process using thehigher gas supply rate should be substantially greater than using theslower gas supply rate. However, in this example, the slower gas flowsare found to provide substantially higher vapor concentration in themixture, and the greater yields obtained under these conditionsdemonstrate the significance of the degree of vapor saturation in thecarrier gas mixture. As will be seen in the Table below, whichsummarizes the results of this experiment, the glass is moved relativeto the gas mixture discharge slot at different speeds and temperaturesare also varied under the most favorable concentration conditions. Thefollowing Table 4 summarizes the results of this example.

TABLE 4 IRON Ill-ACETYLACETONATE: DEPOSlTlON RATES AND YIELDS CarrierGas Vapor Number of Glass Deposit Deposition Supply Rate Pressure SweepsSpeed Microgram Rate Yield Temperature microgram/ 1.min. 10' torrcm.min. (:m. cm.min. C.

7.6 4.3 1 0.2 18.7 3.74 29.7 425 21.8 4.3 l 5 2.08 10.4 28.9 415-42021.8 4.3 1 5 2.39 11.95 33.2 415 420 21.8 4.3 1 2.7 5.3 14.31 39.6415-420 21.8 4.3 1 2.7 3.7 9.98 27.6 415-420 21.8 4.3 l 1.0 6.73 6.7318.6 415-420 21.8 4.3 1 1.0 7.01 7.01 19.4 415-420 21.8 4.3 1 0.5 14.17.05 19.5 415-420 21.8 4.3 1 0.5 14.3 7.15 19.8 415-420 21.8 4.3 l 0.236.9 7.38 20.4 415-420 21.8 4.3 1 0.2 32.0 6.4 17.7 415-420 EXAMPLE vTABLE which decomposition would be massive due.to the autocatalyticeffect already observed.

Since the principles described herein provide a satisfactory rationalefor defining other materials which i could be suitably employed in thepractice of this inlRON Ill-TRIFLUOROACETYLACETONATE DEPOSITION CarrierGas Vapor Number of Glass Deposit Deposition Supply Rate Pressure SweepsSpeed Microgram Rate Yield Temperature microgram/ l.min.' 10* torrcm.min. cm. cm.min. C.

7.6 150 l 5 17.4 87.0 19.1 462 7.6 150 l 5 17.1 85.5 18.8 462 7.6 150 -l10 7.95 79.5 17.5 462 7.6 150 1 10 8.45 84.5 18.6 462 7.6 150 l 5.18103.6 22.8 462 7.6 150 l 20 5.10 102.0 22.4 262 7.6 150 1 42 4.81 202.044.6 462 The principles of this invention may be applied to the vaporcoating of substances which are vaporized from the solid state or whichare first dissolved in an appropriate solvent and then vaporized. In theinstance where the reactants are first dissolved in a solvent, theentropy of vaporization and the degree of saturation of the carrier gasare of great significance, just as they are when the coating reactant isvaporized from the solid state. This is because these factors areresponsible for the sharp and sufficient increase in activity of thecoating reactant immediately adjacent a hot substrate to be coated, sothat-the coating is rapidly deposited, while in a region close to thesubstrate to be coated but out side the thermal barrier, the conditionsof the vapor-gas carrier mixture are such that premature pyrolysis ordecomposition will not occur. When a coating reactant is vaporized fromits solid state, particularly when vaporizing it without firstdissolving it in a solvent, the span of thermal jeopardy shouldpreferably be less than about 140C, and more preferably less than 120C.This factor has particular importance when using a powder vaporizer, forexample, because materials which satisfy this constraint may bevaporized without substantial agglomeration of fused reactant, whichthen heats without breaking up and may prematurely decompose or pyrolyzebefore being fully vaporized,

vention, it is clear that the present invention is not limited to theparticular materials explicitly described herein. Accordingly, thepresent invention is construed to be limited only by the appendedclaims.

We claim: I l. A method of coating a glass substrate with a metal oxidecoating comprising the steps of:

a. dispersing a powdered coating reactant having a standard vaporizationentropy of at least 40 Clausius and a melting point-to-vaporizationpoint span of less than about C. into a stream of air that issufficiently hot to vaporize the coating reactant so that a mixture ofair and vaporized coating reactant is formed;

b. maintaining the mixture at a temperature above that at which it issaturated with the coating reactant and below that at which the coatingreactant pyrolyzes; c. heating the glass substrate to a temperaturesufficient to cause the coating reactant to pyrolyze; and d. deliveringthe mixture sufficiently closely to the hot glass substrate to cause thecoating reactant to pyrolyze forming a coating on the substrate. 2. Themethod according to claim 1 wherein the coating reactant is a metaltrifluoroacetylacetonate.

1. A METHOD OF COATING A GLASS SUBSTRATE WITH A METAL OXIDE COATING COMPRISING THE STEPS OF: A. DISPERSING A POWDERED COATING REACTANT HAVING A STANDARD VAPORIZATION ENTROPY OF AT LEAST 40 CLAUSIUS AND A MELTING POINT-TO-VAPORIZATION POINT SPAN OF LESS THAN ABOUT 120*C. INTO A STREAM OF AIR THAT IS SUFFICIENTLY HOT TO VAPORIZED COATING REACTANT SO THAT A MIXTURE OF AIR AND VAPORIZED COATING REACTANT IS FORMED; B. MAINTAINING THE MIXTURE AT A TEMPERATURE ABOVE THAT AT WHICH IT IS SATURATED WITH THE COATING REACTANT AND BELOW THAT AT WHICH THE COATING REACTANT PYROLYZES; C. HEATING THE GLASS SUBSTRATE TO A TEMPERATURE SUFFICIENT TO CAUSE THE COATING REACTANT TO PYROLYZE; AND D. DELIVERING THE MIXTURE SUFFICIENTLY CLOSELY TO THE HOT GLASS SUBSTRATE TO CAUSE THE COATING REACTANT TO PYROLYZE FORMING A COATING ON THE SUBSTRATE.
 2. The method according to claim 1 wherein the coating reactant is a metal trifluoroacetylacetonate. 